Environmental change impacting on control and transmission of Schistosoma japonicum Schistosomiasis japonica still remains a major public health problem in China today. Results from the 1995 nation-wide sampling survey indicate that 865,000 humans and 100,250 bovines are presently infected with the major endemic foci (accounting for 86% of the total number of people infected in the whole of China) occurring in the marsh and lake regions of Southern China which cover a vast area of five provinces (Jiangsu, Anhui, Hubei, Jiangxi and Hunan). It is anticipated that construction of the giant Three Gorges Dam (TGD) (due to be completed by 2009) across the Yangtze River will have a major impact on the local environment, and substantially alter transmission of schistosomiasis both above and below the dam. What is required to model and predict changes that affect schistosomiasis transmission is to acquire data that complements those we and others have already gathered on the epidemiology of schistosomiasis in China. In this project we will be concerned with how the closure of the Dam will affect the distribution and transmission of schistosomiasis as this will have important consequences impacting on control and control programs in different regions of southern China. In addition we will continue an epidemiologic study that will quantify the role that domestic livestock, especially bovines, play in the transmission of schistosomiasis. The aims of the project are: 1 ). to complete an ongoing TMRC-supported intervention study around the Poyang Lake in Jiangxi Province aimed at proving the hypothesis that bovine, especially buffalo, infections are solely responsible for the persistence of human schistosomiasis transmission in this area of China, 2). to carry out 5 year population-based incidence studies of infection and infection intensity of Schistosoma japonicum infections in humans and livestock, so as to monitor the effect of the closure of the TGD on the distribution and transmission of schistosomiasis in selected areas in the four recognized transmission zones in China, and 3). to utilize retrospective information and the prospective data that will be gathered in this project (and project 2) to mathematically model the impact of the TGD on schistosomiasis transmission and the resulting effect on the cost of effective control strategies in Sichuan (above the Dam), Poyang Lake (below the Dam), Dongting Lake (below the Dam), the Yangtze river isles of Anhui (below the Dam) and the canals of Hubei (below the Dam). The concluding workshop at a recent International Symposium on Schistosomiasis held in China ( 4-July 200 1, Shanghai), under the auspices of the Ministry of Health, remarked on the timeliness and importance of studies along the lines described in this project so as to predict the impact of the closing of the TGD on human schistosomiasis transmission in southern China.